YAMAHA 4HP 4 STROKE high idle when choke of.

[joshhopey]

hi wondering if you could help me i got my self a yamaha 4hp 4 stroke. and when choke is on it idles perfect however when i turn the choke of it idles very high .

i cleaned the carb. however i not 100% sure how many turns main jet / idle jet need? does anyone know this info?

also i been told to replace the intake gaskets ect for air leak ?

[TownsendsFJR1300]

Sounds like an air leak causing a lean condition (which can cause the high idle issue.

Turning on the choke is richening up the fuel mix bringing the A/F mix closer to where it should be..

.

[yamercury]

if its like any other carb it should have a fast idle cam. sounds like even though the choke is open the fast idle cam is not dropping off to allow the throttle to close.. just a hunch.

[TownsendsFJR1300]

if its like any other carb it should have a fast idle cam. sounds like even though the choke is open the fast idle cam is not dropping off to allow the throttle to close.. just a hunch.

We don't know the year of the engine but I've never seen a fast idle cam set up on any Yamaha OB.

Those were common on old school automotive, Rochester carbs, etc..


With a year engine, the exact set up (carb) could be looked and verified..

.

[ausnoelm]

Air leak or carb blockage, clean carb again, properly this time, check all mounting gaskets/seals for damage and go boating.

[99yam40]

Seem like if there is a choke, then there should be something that opens the throttle plates a little also.
got to have air and fuel.
but maybe not, the operator may need to crack the throttle open a little while choking